WASHINGTON -- Lawmakers from both parties urged President Donald Trump's top negotiator in talks over the North American Free Trade Agreement to maintain dispute-resolution mechanisms that have been a central part of the 24-year-old pact.

The dispute-arbitration systems embedded in Nafta have been a flashpoint in the talks, where Mr. Trump's administration has questioned the mechanisms, saying they undermine U.S. sovereignty by allowing the parties to avoid the domestic courts. The lawmakers' lobbying adds to pressure on the administration to retain that component of the agreement.

Many Republicans want to retain, in particular, an arbitration mechanism known as investor-state dispute settlement, which lets companies challenge discriminatory treatment at the hands of a foreign government -- and win compensation.

In the talks, which began last August, the U.S. has proposed scaling back the systems, or allowing the U.S. to opt out of the system. Canada and Mexico have rejected that idea, saying they would prefer to remove the investor-state provision from the three-way Nafta agreement and form their own bilateral investor pact rather than remain a part of a system under Nafta in which different countries have different rights, according to people familiar with the talks.

Lawmakers from the House Ways and Means Committee who met with Robert Lighthizer, the U.S. trade representative, on Wednesday said the dispute-settlement systems are important to companies in their districts because it gives them a way to complain and get compensation for unfair treatment abroad, strengthening their position domestically and internationally. The committee oversees trade issues.

"I want to make sure we hold our trading partners accountable through strong, enforceable commitments with effective dispute settlement...because it creates U.S. jobs," said Rep. Kevin Brady (R., Texas), the committee's chairman. "People in my district and across the country are counting on us to get this right, which is why we all have to stay at the table."

The dispute-resolution issue is one of several that have concerned lawmakers who have companies or farms in their districts that have benefited from the export markets Nafta has created and want to preserve the beneficial parts of the trade pact.

Still, some GOP lawmakers agree with Mr. Trump, a fellow Republican, that past trade agreements have ceded too much U.S. sovereignty. Some lawmakers in industrial areas blame trade with China and Mexico for moving U.S. jobs abroad.

"We've had it with jobs getting sent overseas and the cheating of foreign competitors like China," said Rep. Walter Jones (R., N.C.). "President Trump pledged to fix that, and the actions taken thus far have been encouraging."

The talks, which are scheduled to resume later this month in Mexico, are only beginning to tackle some of the most contentious issues, a pace that has worried some pro-Nafta lawmakers.

One Democrat said Wednesday that Mr. Lighthizer floated the idea of wrapping up talks with Mexico and continuing longer-term talks with Canada. The administration has blamed Canada for adding unacceptable demands and boosting tension in the talks.

"He would not be dissatisfied with doing a bilateral [agreement] with Mexico," said Rep. Ron Kind (D., Wis.), a backer of existing trade agreements and critic of the administration's policy.

A congressional aide said the idea of a bilateral deal with Mexico is likely a step to put pressure on Ottawa and won't go anywhere unless Mexico City embraces one-on-one talks with the U.S.

Rep. Sandy Levin (D., Mich.) said Mexico is "moving in the wrong direction" on the labor issue but added the administration "has disagreements with Canada."

Mr. Lighthizer declined to answer questions after leaving the meeting, and a spokeswoman for his office declined to comment. At the start of Nafta negotiations, Mr. Lighthizer said his preference was to preserve the three-nation structure of Nafta but that some issues could be negotiated bilaterally. The administration has generally backed one-on-one trade negotiations that it believes maximize U.S. leverage.

During the past year, Democratic lawmakers have expressed enthusiasm about the direction of trade under Mr. Trump, who has threatened to impose barriers at the border to block unfair trade imports.

The dispute-resolution debate, however, threatens that support, as Democrats want to make strengthened labor provisions in a renegotiated Nafta fully binding. On the eve of the latest round of Nafta talks last month in Montreal, more than 180 House Democrats pressed for stronger labor standards as a way of raising wages in Mexico.

Senate Republicans are planning to discuss trade at a White House meeting Wednesday afternoon. "I was encouraged by the recent Nafta talks in Montreal and I will continue to be the voice of America's farmers and ranchers in the president's ear," said Sen. Pat Roberts (R., Kan.), in a statement.

U.S. Agriculture Secretary Sonny Perdue expressed optimism this week that a Nafta deal could be included by the end of the year. But business groups following the talks said they are concerned that a presidential election in Mexico and the U.S. midterm elections are making it difficult to reach a deal because any public concessions could hurt politicians in their home countries.